A dialysis dose is defined as a therapeutic dose of one hemodialysis treatment applied to a patient. As indexes of the dialysis dose, there are two indexes, i.e., a urea removal rate (R) and a Kt/V (=f(R)) value. In general, the Kt/V value is adopted. The Kt/V value of hemodialysis treatment is conventionally calculated by substituting, in a predetermined formula, serum urea concentrations measured at the start and at the end of hemodialysis treatment, a water removal volume during the hemodialysis treatment, and a treatment time of the hemodialysis treatment after completion of the hemodialysis treatment.
The serum urea concentration at the end of the hemodialysis treatment for calculating the Kt/V value can be determined by six factors, i.e., a body fluid volume, which is a total volume of water in the body of the patient, a hemodialysis treatment time, a water removal volume during the hemodialysis treatment, a mass-transfer area coefficient (in general, referred to as “K0A”), which is an index indicating the performance of a dialyzer in use, blood flow velocity, and dialysis fluid flow velocity.
Incidentally, at present, a Kt/V value for minimizing a death rate, a so-called optimum Kt/V value, has been clarified by a large number of statistical surveys and researches. In hemodialysis treatment, it is necessary to execute hemodialysis treatment with which the optimum Kt/V value clarified by the large number of statistical surveys and researches can be attained. Therefore, usually, a medical staff member adjusts at least the blood flow velocity or the dialysis fluid flow velocity as an adjustment factor at the start of the hemodialysis treatment to thereby resultantly adjust the Kt/V value through adjustment of the serum urea concentration at the end of the hemodialysis treatment.
More specifically, at present, a hemodialysis facility first sets the optimum Kt/V value as a target Kt/V value. Then, the hemodialysis facility substitutes, in a predetermined formula, measured serum urea concentrations at the start and at the end of hemodialysis treatment in the past, a water removal volume during the same hemodialysis treatment, and a treatment time of the same hemodialysis treatment to calculate a Kt/V value of the hemodialysis treatment in the past. Then, after comparing the Kt/V value in the hemodialysis treatment in the past and the target Kt/V value, the hemodialysis facility adjusts, through trial and error, blood flow velocity or dialysis fluid flow velocity in hemodialysis treatment to be carried out while referring to blood flow velocity or dialysis fluid flow velocity in the hemodialysis treatment in the past such that a Kt/V value of the hemodialysis treatment to be carried out reaches the target Kt/V value.
The adjustment of the blood flow velocity and the dialysis fluid flow velocity is performed on the basis of a prediction through data of hemodialysis treatment in the past, empirical rules, and the like as explained above. Therefore, in reality, it is difficult to accurately attain the target Kt/V value as the Kt/V value of the hemodialysis treatment. Further, for example, the water removal volume, which is the factor for determining serum urea concentration at the end of the hemodialysis treatment and is used for calculation of the Kt/V value, changes in each hemodialysis treatment. A relation between the blood flow velocity and the Kt/V value in the hemodialysis treatment also changes for each patient and according to a dialyzer in use. Moreover, values of the other factors affecting the Kt/V value unpredictably change in this way. Therefore, even if the blood flow velocity and the dialysis fluid flow velocity are adjusted according to the data in the past and the like as explained above, it is difficult to accurately attain the target Kt/V value after the end of the hemodialysis treatment.
As a method for solving this problem, a method has been developed for calculating, by analyzing a mathematical model concerning urea kinetics, a body fluid volume, which is a total volume of water in a body of a patient, from measured serum urea concentration at the start of specific hemodialysis treatment and measured serum urea concentration at the end of the hemodialysis treatment, a dialysis treatment time of the hemodialysis treatment, a water removal volume during the hemodialysis treatment, blood flow velocity in the hemodialysis treatment, dialysis fluid flow velocity in the hemodialysis treatment and a mass-transfer area coefficient of a dialyzer used in the hemodialysis treatment during specific hemodialysis treatment and then during the hemodialysis treatment carried out after the specific hemodialysis treatment, kinetics dialysis fluid flow velocity necessary for attaining the target Kt/V value from the body fluid volume which had been calculated during the specific hemodialysis treatment and a planned dialysis treatment time, a planned water removal volume, blood flow velocity, a mass-transfer area coefficient of a dialyzer in use and the target Kt/V (Non-Patent Literature 1). According to this method, it is possible to more surely calculate dialysis fluid flow velocity for attaining the target Kt/V value for hemodialysis treatment to be performed.